This invention relates generally to gas turbine engines, and more specifically to igniter tubes used with gas turbine engine combustors.
Combustors are used to ignite fuel and air mixtures in gas turbine engines. Known combustors include at least one dome attached to a combustor liner that defines a combustion zone. More specifically, the combustor liner includes an inner and an outer liner that extend from the dome to a turbine nozzle. The liner is spaced radially inwardly from a combustor casing such that an inner and an outer passageway are defined between the respective inner and outer liner and the combustor casing.
Fuel igniters extend through igniter tubes attached to the combustor outer liner. More specifically, the fuel igniter tubes extend through the outer passageway and maintain the igniters in alignment relative to the combustion chamber.
During operation, high pressure airflow is discharged from the compressor into the combustor where the airflow is mixed with fuel and ignited with the igniters. A portion of the airflow entering the combustor is channeled through the combustor outer passageway for cooling the outer liner, the igniters, and diluting a main combustion zone within the combustion chamber. Because the igniters are bluff bodies, the airflow may separate and wakes may develop downstream from each igniter. As a result of the wakes, a downstream side of the igniters and igniter tubes is not as effectively cooled as an upstream side of the igniters and igniter tubes which is cooled with airflow that has not separated. Furthermore, as a result of the wakes, circumferential temperature gradients may develop in the igniter tubes. Over time, continued operation with the temperature gradients may induce potentially damaging thermal stresses into the combustor that exceed an ultimate strength of materials used in fabricating the igniter tubes. As a result, thermally induced transient and steady state stresses may cause low cycle fatigue (LCF) failure of the igniter tubes.
Because igniter tube replacement is a costly and time-consuming process, at least some known combustors increase a gap between the igniters and the igniter tubes to facilitate reducing thermal circumferential stresses induced within the igniter tubes. As a result of the gap, leakage passes from the passageways to the combustion chamber to provide a cooling effect for the igniter tubes adjacent the combustor liner. However, because such air is used in the combustion process, such gaps provide only intermittent cooling, and the igniter tubes may still require replacement.
In an exemplary embodiment, a combustor for a gas turbine engine includes a plurality of igniter tubes that facilitate reducing wake temperatures and temperature gradients within the combustor in a cost effective and reliable manner. The combustor includes an annular outer liner that includes a plurality of openings sized to receive igniter tubes. Each igniter tube maintains an alignment of each igniter received therein, and includes an air impingement device that extends radially outward from the igniter tube.
During operation, airflow contacting the air impingement device is channeled radially inward towards an aft end of the igniter tubes and towards the combustor outer liner. More specifically, the airflow is directed circumferentially around the igniter tubes for impingement cooling the igniter tube and the surrounding combustor outer liner. The impingement cooling facilitates reducing overall wake temperatures and circumferential temperature gradients in the igniter tubes and the combustor outer liner. As a result, lower thermal stresses and therefore improved low cycle fatigue life of the igniter tubes are facilitated in a cost-effective and reliable manner.